A row between Gordon Brown and the leader of the Scottish Labour party over an independence referendum intensified yesterday, amid deepening confusion over government policy towards a vote. As the Tories accused Labour of endangering the UK's future, Wendy Alexander appeared to defy the prime minister by intensifying demands for an immediate poll.

"I and my colleagues have ... offered our support to bring this issue forward now," Alexander said in noisy exchanges in the Scottish parliament at Holyrood. Her remarks undermined Brown's central defence in the row: that Alexander was not calling for an immediate poll.

When the Tory leader, David Cameron, asked in the Commons on Wednesday whether Brown supported Alexander's "referendum now" call, the prime minister replied: "That is not what she has said. What the leader of the Labour party in Scotland was pointing to was the hollowness of the Scottish National party, which said that it wanted independence, said that it wanted it immediately, and now wants to postpone a referendum until 2010-11."

Cameron last night accused the prime minister of losing control of his party. In his second letter to the prime minister on the matter in 24 hours, he wrote: "Anyone comparing what you have claimed, and what Wendy Alexander has repeated this morning, will conclude that either you have been completely unclear and misleading in your replies to my questions, or you have lost control of your party - or perhaps, it is a combination of the two."

The furore came as a YouGov opinion poll put the Tories 26 points ahead of Labour, whose support fell to a record low of 23%.

Senior Labour sources in London indicated that Brown was furious with Alexander, who did not inform the prime minister before she issued a "bring it on" challenge to the SNP on Sunday. Alexander repeated this challenge yesterday when she told Scottish parliament that the SNP administration should act now. With most Labour backbenchers cheering her, she said: "The first minister has a statement next week on his programme for government. The question is simply: will he bring forward a referendum bill in next year's legislative programme next week?"

One senior Labour figure in London said: "Is Wendy Alexander damaged? Yes. Is Gordon Brown damaged? Yes. Is the Labour party damaged? Yes. Is Alex Salmond strengthened? Yes. Wendy did not tell Gordon about her announcement ... This is Wendy Alexander incorporated."

Salmond mocked Alexander for hastening Scottish independence. But he rejected her invitation to hold an immediate referendum and insisted his SNP administration would keep to its manifesto pledge to wait until 2010. "It is impossible for anyone outside the Labour party - and I think most people in it - to take the Labour party seriously after the last few days," he said.

If the bill is passed in Holyrood the Westminster parliament will face strong political, but not legal, pressure to pass legislation granting a referendum. Only Westminster can sanction referendums on Scotland's place in the UK.

There are signs that Brown's anger over this conflict has forced the Scottish Labour party to soften its stance on the forthcoming bill. Earlier this week, senior party officials implied that Scottish Labour could even vote for a referendum. Labour MSPs now insist privately that this means, at the very most, that they would abstain on the bill and could even vote against it if the wording of the referendum question was too imbalanced.

Scottish Labour MSPs publicly endorsed their leader's stance, however, and insisted there was no conflict between her challenge to the SNP and Brown's statements on Wednesday.

The Tories accused Labour of endangering the union. David Mundell, the shadow Scottish secretary, said: "Gordon Brown's persistent dithering is putting the union at risk."

Backstory

Wendy Alexander and Gordon Brown agree on one point: Scotland should remain in the UK. But they disagree on whether, and when, a referendum on independence should be held. Brown believes it should not be discussed until the Calman commission, which is considering the future of the Scottish Parliament, has reported. Alexander believes an immediate referendum would wrongfoot Alex Salmond, the SNP leader, who wants to wait until 2010. Salmond hopes a successful SNP administration will increase support for independence, which one recent poll put at 19%.